200 GHz Maximum Oscillation Frequency in CVD Graphene Radio Frequency Transistors

Abstract

Graphene is a promising candidate in analog electronics with projected operation frequency well into the terahertz range. In contrast to the intrinsic cutoff frequency (f) of 427 GHz, the maximum oscillation frequency (f) of graphene device still remains at low level, which severely limits its application in radio frequency amplifiers. Here, we develop a novel transfer method for chemical vapor deposition graphene, which can prevent graphene from organic contamination during the fabrication process of the devices. Using a self-aligned gate deposition process, the graphene transistor with 60 nm gate length exhibits a record high f of 106 and 200 GHz before and after de-embedding, respectively. This work defines a unique pathway to large-scale fabrication of high-performance graphene transistors, and holds significant potential for future application of graphene-based devices in ultra high frequency circuits.

High-Gain Graphene Transistors with a Thin AlOx Top-Gate Oxide

“…The highest measured extrinsic was 21.3 GHz in a GFET with W  = 10  μ m and L  = 1  μ m (discussion on the intrinsic can be found in the Supplementary information). The obtained values are comparable to those of GFETs with the same gate length 14, 16, 28 . Even though it has previously been found that does not scale very well with the gate length in GFETs 28 , we observed a gate-length dependence down to 0.8  μ m, despite noticeable degradation in submicron devices.…”

“…As a consequence, the output conductance ( g d ) was reduced well below 50 S/m (normalized by the channel width W ) leading to very large values of the open-circuit voltage gain A v  > 30 dB and forward gain S 21  = 12.5 dB (at 10 MHz) in GFETs with the channel widths W  = 10  μ m and W  = 100  μ m, respectively, which are the highest gains measured in GFETs so far 9–12 . This low output conductance also contributed to a large ratio between the extrinsic maximum oscillation frequency ( f max ) and cutoff frequency ( f T ) of ~3, which is unusually high for GFETs, in which f max / f T typically ranges from <1 13, 14 to ~1.5 15, 16 to 3.3 17 . However, the highest measured extrinsic f max was 21.3 GHz highlighting the need for alternative substrates with less charge traps 14 and cleaner graphene transfer process 16 .…”

“…This low output conductance also contributed to a large ratio between the extrinsic maximum oscillation frequency ( f max ) and cutoff frequency ( f T ) of ~3, which is unusually high for GFETs, in which f max / f T typically ranges from <1 13, 14 to ~1.5 15, 16 to 3.3 17 . However, the highest measured extrinsic f max was 21.3 GHz highlighting the need for alternative substrates with less charge traps 14 and cleaner graphene transfer process 16 .…”

A graphene based frequency quadrupler

“…On the other hand, both contact resistance and channel resistance make contribution to output resistance of GFET. A polymeric residue-free graphene fabrication process50 can be carried out to reduce contact resistance. Channel resistance can be decreased by fabricating GFET with nanoscale channel length and large W/L ratio.…”

Monolithic optoelectronic integrated broadband optical receiver with graphene photodetectors

“…As potential carrier mobility of graphene is extremely high, the operation bandwidth of GPD is limited by RC constant of the device structure and a 500 GHz [21] intrinsic operation speed can be achieved in the future. Although the first graphene-based optical receiver achieved in this work just works at 500 kHz with 1550 nm carrier waves, the performance can be improved significantly if a single crystal graphene with higher carrier mobility is used and an optimized fabrication process [45] is carried out to reduce contact resistance and remove residue on the graphene surface. In addition, further collaborative parameter optimization of the TIA chips and GPDs may increase the operation speed to a great extent.…”